Study on the antioxidant capacity of the melanin from walnut shell and walnut epicarp

In order to explore the comprehensive value of the discarded walnut remains, this study evaluated the antioxidant capacity of the melanin extracted from walnut shell and walnut epicarp with NaOH as extracting solvent.The total anti-oxidative activity was investigated by the reducing capacity and the scavenging activity of radicals of·OH, O-2· and DPPH· which compared with the synthetic antioxidant BHT.The structure of melanin was determined by infrared spectroscopy and compared with other studies.The results showed that melanin from walnut shell and walnut epicarp exhibited reducing capacity and played an important role in removing ·OH, O-2·, DPPH·.The reducing capacity increased with the increasing concentration.When the concentration was above 0.06mg/mL the reducing capacity of the melanin from walnut epicarp was better than that of the melanin from the walnut shell, but was weaker than BHT.The IC50 of the melanin from walnut shell scavenged the ·OH was 0.46mg/mL, while the melanin from the walnut epicarp was 0.12mg/mL.The IC50 of the melanin from walnut epicard scavenged O-2· was 0.54mg/mL, while the melanin from the walnut epicarp was 0.30mg/mL.When the concentration of the melanin from walnut epicard reached 0.8mg/mL the scavenging rate on O-2· reached to 94.6% which closes to that of VC with the same concentration, and the scavenging rate on DPPH· attained to 84.14% when the concentration was 0.2mg/mL.According to infrared spectroscopy melanin from walnut shell and walnut epicarp had similar structures containing phenolic compounds, amine compounds, alcohols, and aromatic compounds, and the anti-oxidative activity depended on the ability of providing hydrogen of the samples.